Orientation stabilization for MEMS devices

Abstract

A control circuit designed to control driving voltages applied to the actuating electrodes of a MEMS mirror. The control circuit is interfaced with a mirror position sensor and includes a variable gain amplifier whose output depends on a desired mirror equilibrium angle and a current mirror tilt angle determined by the sensor. The desired equilibrium angle can be changed by varying a reference signal applied to the amplifier. The control circuit can stabilize the mirror at relatively large tilt angles and, as a result, extend the available angular range beyond the snap-down angle. Since the number of MEMS mirrors that can be arrayed in an optical cross-connect is a function of the available angular range, the number of channels in a cross-connect may be substantially increased.

What is claimed is:  
     
       1. Apparatus, comprising: 
       a MEMS device; and  
       a controller adapted to:  
       receive, from a position sensor corresponding to the MEMS device, a sensor signal indicative of a current position of a movable part of the MEMS device with respect to a stationary part of the MEMS device; and  
       generate a control signal as a function of the sensor signal, wherein an actuator of the MEMS device is adapted to achieve a desired position of the movable part with respect to the stationary part based on the control signal, wherein the control signal has a voltage profile, wherein a first portion of the voltage profile has voltage having an absolute value greater than a snap-down voltage for the MEMS device.  
     
     
       2. The invention of  claim 1 , wherein a second portion of the voltage profile has voltage varying substantially linearly with a current rotation angle between the movable and stationary parts. 
     
     
       3. The invention of  claim 1 , wherein a second portion of the voltage profile has voltage corresponding to a substantially constant electrostatic torque applied to the movable part with respect to the stationary part. 
     
     
       4. The invention of  claim 1 , wherein the MEMS device forms part of an optical switch. 
     
     
       5. Apparatus, comprising 
       a MEMS device; and  
       a controller adapted to:  
       receive, from a position sensor corresponding to the MEMS device, a sensor signal indicative of a current position of a movable part of the MEMS device with respect to a stationary part of the MEMS device; and  
       generate a control signal as a function of the sensor signal, wherein an actuator of the MEMS device is adapted to achieve a desired position of the movable part with respect to the stationary part based on the control signal, wherein:  
       the movable part is rotatably coupled to the stationary part;  
       the sensor signal is indicative of a current rotation angle between the movable and stationary parts;  
       the control signal is a function of the current rotation angle;  
       the desired position corresponds to an equilibrium rotation angle between the movable and stationary parts; and  
       the control circuit is adapted to generate the control signal based on the sensor signal and a reference signal corresponding to the equilibrium rotation angle.  
     
     
       6. The invention of  claim 5 , wherein an adjustment of the reference signal corresponds to a change in the equilibrium rotation angle. 
     
     
       7. The invention of  claim 5 , wherein the equilibrium rotation angle is greater than or substantially equal to a snap-down angle for the MEMS device. 
     
     
       8. The invention of  claim 5 , wherein the MEMS device forms part of an optical switch. 
     
     
       9. The invention of  claim 5 , wherein the control circuit comprises a first amplifier adapted to: 
       receive the reference signal and a fourth signal based on the sensor signal; and  
       generate a fifth signal, wherein the control signal is based on the fifth signal.  
     
     
       10. The invention of  claim 9 , wherein the fourth signal is a substantially linear function of the current rotation angle. 
     
     
       11. The invention of  claim 9 , wherein the control circuit further comprises a second amplifier adapted to amplify the fifth signal to generate the control signal. 
     
     
       12. The invention of  claim 9 , wherein the first amplifier comprises: 
       an operational amplifier adapted to operate as an inverting adder; and  
       a voltage regulator connected to an output of the operational amplifier, wherein:  
       the operational amplifier is adapted to receive the reference and fourth signals; and  
       the fifth signal is a regulated output signal of the operational amplifier.  
     
     
       13. The invention of  claim 12 , wherein the voltage regulator is adapted to clip the output signal of the operational amplifier if the output signal is more negative than a base voltage of the voltage regulator. 
     
     
       14. Apparatus, comprising: 
       means for receiving, from a position sensor corresponding to a MEMS device, a sensor signal indicative of a current rotation anile between a movable part of the MEMS device and a stationary part of the MEMS device; and  
       means for generating a control signal based on the sensor signal and a reference signal, wherein:  
       the movable part is rotatably coupled to the stationary part;  
       the control signal is a function of the current rotation angle;  
       the reference signal corresponds to an equilibrium rotation angle between the movable and stationary parts;  
       an actuator of the MEMS device achieves the equilibrium rotation angle based on the control signal; and  
       the equilibrium rotation angle is greater than or substantially equal to a snap-down angle for the MEMS device.  
     
     
       15. Apparatus, comprising: 
       means for receiving, from a position sensor corresponding to a MEMS device, a sensor signal indicative of a current rotation angle between a movable part of the MEMS device and a stationary part of the MEMS device; and  
       means for generating a control signal based on the sensor signal and a reference signal, wherein:  
       the movable part is rotatably coupled to the stationary part;  
       the control signal is a function of the current rotation angle;  
       the reference signal corresponds to an equilibrium rotation angle between the movable and stationary parts;  
       an actuator of the MEMS device achieves the equilibrium rotation angle based on the control signal; and  
       means for adjusting the reference signal to change the equilibrium rotation angle.  
     
     
       16. A method comprising: 
       receiving, from a position sensor corresponding to a MEMS device, a sensor signal indicative of a current rotation angle between a movable part of the MEMS device and a stationary part of the MEMS device; and  
       generating a control signal based on the sensor signal and a reference signal, wherein:  
       the movable part is rotatably coupled to the stationary part;  
       the control signal is a function of the current rotation angle;  
       the reference signal corresponds to an equilibrium rotation angle between the movable and stationary parts; and  
       an actuator of the MEMS device achieves the equilibrium rotation angle based on the control signal; and  
       adjusting the reference signal to change the equilibrium rotation angle.  
     
     
       17. The invention of  claim 16 , wherein the MEMS device forms part of an optical switch. 
     
     
       18. A method comprising: 
       receiving, from a position sensor corresponding to a MEMS device, a sensor signal indicative of a current rotation angle between a movable part of the MEMS device and a stationary part of the MEMS device; and  
       generating a control signal based on the sensor signal and a reference signal, wherein:  
       the movable part is rotatably coupled to the stationary part;  
       the control signal is a function of the current rotation angle;  
       the reference signal corresponds to an equilibrium rotation angle between the movable and stationary parts;  
       an actuator of the MEMS device achieves the equilibrium rotation angle based on the control signal; and  
       the equilibrium rotation angle is greater than or substantially equal to a snap-down angle for the MEMS device.  
     
     
       19. The invention of  claim 18 , wherein the MEMS device forms part of an optical switch.